Auto merge of #112645 - Kobzol:ci-mingw-merge, r=pietroalbini

CI: merge `mingw` test CI jobs

Same as rust-lang/rust#112633, but for `mingw`. From the logs it looks like the runner spends 40 minutes compiling `rustc`, and then `10`/`20` minutes running tests. It seems wasteful to split that into two jobs.

CI run: https://github.com/rust-lang/rust/actions/runs/5275702134/jobs/9541479343?pr=112645

r? `@jyn514`

Author: bors